1. Field of the Invention
The present invention relates generally to a polarization measuring apparatus in a mobile communication system. In particular, the present invention relates to a polarization measuring apparatus in a mobile radio communication system which can accurately measure a polarized wave of a code division multiple access (CDMA) signal.
2. Description of the Related Art
Generally, a radio wave is polarized. This means that the direction of an electric field, which is perpendicular to the forwarding direction of propagation of the radio wave, leans to a specific direction. This appearance is called polarization.
Particularly, in wireless communications, the polarization is a very important factor when an antenna is selected and installed. The polarized wave is classified into a linearly polarized wave, a circularly polarized wave, etc.
The linearly polarized wave has a constant plane of polarization having the direction of the electric field and the propagation direction. Specifically, a horizontally polarized wave has the polarization plane parallel to the ground, and a vertically polarized wave has the polarization plane perpendicular to the ground.
The circularly polarized wave is a wave wherein an electric field vector, which represents the magnitude and direction of the electric field on the plane perpendicular to the propagation direction, rotates in a constant direction. As one of the circularly polarized wave exists an elliptically polarized wave wherein an elliptical trace is drawn by the terminal point of the electric field vector.
The elliptically polarized wave has various properties, and factors representing such properties are axial ratios, tilt angles, etc.
The axial ratio is also called an ellipticity, and represents the difference between the maximum and minimum peaks of the electric field vector rotating through all angles, i.e., the ratio of an electric field intensity in the direction of a major axis to that in the direction of a minor axis. Also, the tilt angle represents the tilting extent of the major axis for a specific criterion axis.
In a mobile communication system, it is required to accurately measure the polarization. Especially, in case of a mobile communication system using a high frequency band such as a personal communication service (PCS) system and a next-generation mobile communication system, it is important to perform the accurate modeling of the wave propagation by an accurate polarization measurement and also to realize a polarization diversity.
Here, the polarization diversity is for removing unstable characteristics such as fading by radiating from vertical and horizontal antennas radio waves having different leans from each other. In order to realize the polarization diversity, antenna installation variables such as the directional angle of the antennas, length of the antennas, etc. are first determined, and then the antennas are installed considering the determined variables.
The polarization measuring apparatus of the mobile communication system performs the polarization measurement required for the accurate modeling of the wave propagation and the determination of the antenna installation variables as described above.
FIG. 1 is a view illustrating the construction of a conventional polarization measuring apparatus.
As illustrated in FIG. 1, the conventional polarization measuring apparatus includes a linear antenna 1 and a received power measuring instrument 2.
The linear antenna 1 is rotatable by 360xc2x0, and is connected to the received power measuring instrument 2 by power lines.
The received power measuring instrument 2 measures the power value of a received wave at the respective rotational positions of the linear antenna 1. Thus, the polarization property of the received wave is obtained by measuring the rotational angle when the power value of the radio wave incident to the linear antenna 1 rotating by 360xc2x0 is maximum.
As a result, only information on the linearly polarized wave with a constant plane of polarization having the electric field direction and the propagation direction is provided due to the constructional characteristic of the conventional polarization measuring apparatus.
Accordingly, it is impossible to accurately measure the information on various polarized waves which may be produced if a wide frequency band signal such as the CDMA signal is used.
Also, no equipment has been developed for measuring such an accurate information on the elliptically polarized wave wherein the electric field direction occasionally varies with respect to the propagation direction though such an accurate information is required in order to perform the accurate modeling of the propagation and to realize the polarization diversity in the CDMA environment where a number of scattering substances exist.
Accordingly, the present invention is directed to a polarization measuring apparatus in a mobile communication system that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a polarization measuring apparatus in a mobile communication system which can measure the property of an elliptically polarized wave of a received radio wave as well as the property of a linearly polarized wave.
It is another object of the present invention to provide a polarization measuring apparatus in a mobile communication system which can measure the polarization property of the received radio wave more accurately by compensating for the error of internal radio frequency (RF) elements used for the polarization measurement and the loss on internal paths produced during the polarization measurement.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the mobile communication system according to the present invention includes a polarization measuring apparatus for receiving power values of vertical and horizontal elements of an incident electric field for a received radio wave and measuring various polarization power values of the incident electric field, and a computer for receiving the measured polarization power values and analyzing polarization properties of the received radio wave.
The polarization measuring apparatus comprises a dual polarization antenna for outputting the power values of the vertical and horizontal elements of the incident electric field of the received radio wave, a polarization switch for switching to and outputting through different paths the power values of the respective elements of the incident electric field inputted from the dual polarization antenna, and a spectrum analyzer for measuring the respective polarization power values outputted from the polarization switch.
The polarization measuring apparatus further comprises a signal generator for generating a test signal having predetermined power value and frequency, an internal calibration block for outputting various polarization power values for the test signal provided from the signal generator by switching the test signal to the different paths, a first directional coupler for selectively outputting one of the vertical element power value of the incident electric field inputted from the dual polarization antenna and one polarization power value inputted from the internal calibration block, and a second directional coupler for selectively outputting one of the horizontal element power value of the incident electric field inputted from the dual polarization antenna and the other polarization power value inputted from the internal calibration block.
The computer calculates an ellipticity and a tilt angle of polarization of the received radio wave using the various polarization power values of the incident electric field provided from the polarization measuring apparatus and compensation information for the error of internal radio frequency (RF) elements and for the loss on internal paths of the polarization measuring apparatus.